In recent years, high wet grip performance and low rolling resistance have been demanded for pneumatic tires. To satisfy these, technologies in which a styrene-butadiene copolymer and a reinforcing filler such as silica are blended in a rubber composition constituting a cap tread of a tire have been known. Furthermore, to enhance wear resistance, rubber hardness, and modulus of repulsion elasticity of a rubber composition, for example, blending of polybutadiene and/or highly reactive silica has been proposed; however, in this case, problems of reduction in rubber strength, deterioration of processability, and the like existed.
Japanese Unexamined Patent Application Publication No. 03-239737A describes that a pneumatic tire manufactured using a rubber composition containing a styrene-butadiene copolymer having a particular arrangement of styrene-derived units, and silica in a tread can satisfy wet skid resistance, rolling resistance, and wear resistance at the same time. However, this rubber composition cannot always enhance wear resistance and low heat build-up and thus could not fully satisfy the demands from consumers.
Japanese Unexamined Patent Application Publication No. 57-179212 describes a styrene-butadiene copolymer in which, relative to a total styrene content in a styrene-butadiene copolymer, a long chain styrene block is 5 wt. % or less and one single chain is 50 wt. % or greater in styrene-derived units, and a total content of styrene is 10 to 30 wt. % of the styrene-butadiene copolymer. However, this is not sufficient to enhance rubber strength, wear resistance, and low hysteresis loss of rubber compositions.